The foregoing expressions illustrate the use of the cut conjunction (;.)
to apply the functions sum (+/) and box (<) over partitions or
fields of the right argument y demarked by the boolean left
argument x.
The case of the box gives a clear picture of the partitioning performed;
in case 1, the ones in the left argument mark the beginnings of fields,
and in case 2 they mark the ends.

A function (such as the sum scan) that produces non-scalar results illustrates
the fact that the box of such a function provides a more readable result: